Gelatin silver halide emulsion plasticized with dicarboxylic acid esters



GELATIN SILVER HALIDE EMULSION PLASTI- CIZED DICARBOXYLIC ACID ESTERSGlen G. Gray, Rochester, N.Y., assignor to Eastman K- dak Company,Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Aug. 16,1956, Ser. No. 604,333

3 Claims. (CI. 96-94) graphic industry with respect to coatingphotographic \base have been the tendency for gelatin and other similarmaterials to foam due to the air which becomes entrained in-handlingmixtures of these materials, the tendency of emulsion layers to curl andcrack in low humidities due to the, brittleness of the emulsion layers,and the tendency of paper and film to become statically charged and todischarge across a photographic emulsion causing static streaks.

Various methods have been suggested to meet the problem of foamingincluding passing solutions containing gelatin under a vacuum in orderto remove entrained air, adding certain wetting agents in an effort toreduce the surface tension of the gelatin to permit air to escape, andthe like. Various methods have been used in an attempt to reduce thecurl of photographic prints such as immersing the finished prints insolutions or steaming the back of the paper. added to lower theelectrical surface resistivities of the paper and film in order toreduce the static charge built up in the paper webs and film as theypass through various operations such as emulsion coating, rewinding,slitting, chopping and the like. For instance, British Patent 709,555describes the use of long chain fatty acid partial esters of aliphaticpolyhydric alcohols. Glycerin has been used to plasticize photographicemulsions. The above operations using conventionalmethods have requiredthe use of difierent compositions for accomplishing each of thesepurposes and, consequently, it has been desired to fined a simple meansof solving all three problems with a single chemical composition.

I have discovered that a certain ester of a glycol ether can be used asan anti-foaming agent for gelatin and other spumous materials, as aplasticizer for gelatin used in coating paper for photographic purposes,as a plasticizer in gelatino photographic emulsions and as an agent forlowering the surface resistivities and correspondingly reducing thetendency of paper and film to build up static charges.

An object of this invention is to provide a process for reducing foamingof gelatin emulsions, for stabilizing paper and for improving theelectrification properties of paper and film using a single chemicalcomposition. Another object of this invention is to stabilizephotographic paper by reducing the curl and emulsion cracking. A furtherobject of this invention is to provide an antifoaming agent for gelatinand other spumous materials. An additional object is to provide a methodof improving Certain compositions have been 2,940,854 Patented June 14,1960 the electrification properties of paper and film. A further Iobject is to provide a gelatin plasticizer.

The above objects may be accomplished by using a composition of matterprepared as described in column 3, lines 943 by esterification ofsuccinic acid with a mixture of 2(2-ethoxy ethoxy) ethanol and ethyleneglycol. This mixture of reaction products is intended when reference ismade herein to bis(ethoxy diethylene glycol) succinate.

By substituting dibasic acids selected from the class consisting ofsuccinic, adipic, and phthalic acids and by substituting diethyleneglycol monoalkyl ethers in which the alkyl group may be lower alkyl suchas ethyl, propyl or butyl, other reaction products mixtures may beobtained which are also operative in my invention.

To use this material as an anti-foaming agent, the bis (ethoxydiethylene glycol) succinate is added to emulsions or dispersionscontaining gelatin vehicles in which entrained air causes foaming. Forinstance, when baryta dispersions containing gelatin are drawn from themaking kettles into the holding kettles at the coating machines, or intothe coating pans, or are recirculated by pumps in the coating pans, aconsiderable quantity of foam develops. If foaming is extensive andcarries over into the coated layer, small craters appear as theentrained air escapes during drying.

The bis (ethoxy diethylene glycol) succinate can be added in the makingkettle or at some other point prior to coating. However, the addition ofthis material may be made most conveniently in the making kettle, atwhich point it acts to reduce foam in the subsequent operations.

Bis (ethoxy diethylene glycol) succinate may be used to reduce curl andemulsion cracking in photographic papers by adding it to the barytacoating when the coating composition is prepared in the making kettles.In this way the pigment layer is plasticized and the stresses andstrains of both the emulsion layer on top of the pigment layer and thepaper base beneath the pigment layer are lessened. Bis (ethoxydiethylene glycol) succinate is compatible with mineral pigmentdispersions, with the gelatin and is also photographically inert. In theevent porating it in the coating, a subsequent treatment may be given tothe paper to accomplish this purpose. The paper may be immersed in asolution of his (ethoxy diethylene glycol) succinate in order toincorporate this material in the paper base as Well as in the pigmentlayer, in this Way also stabilizing the paper against curl.

The electrification properties of paper are improved by the addition ofhis (ethoxy diethylene glycol) succinate in the paper coating, and thetendency of the static charge to build up is decreased. When a web ofpaper travels at a relatively high speed on mechanical equipmentinvolving carrying rolls in contact With the paper, a static charge ofelectricity builds up until a sufiicient potential is obtained to causean electrical discharge. The magnitude of the static charge increaseswith decreasing relative humidity, and increasing electrical resistanceof the paper. I

The build up of static charges in paper webs is always objectionable;however, in the case of photographic papers, the discharge of staticelectricity during opera tions such as, emulsion coatings, rewinding,slitting, chop ping and the like can fog light-sensitive emulsionlayers. Although bis (ethoxy diethylene glycol) succinate can beincorporated in the coating composition, it may also be applied byimmersing the paper in a solution in ethanol, Water, or similar solvent.

The agents which I have described such as his (ethoxy diethylene glycol)succinate, may be used as plasticizers in various kinds of photographicemulsions, In addition to being useful in non-sensitized emulsions, theymay also be used in positive speed emulsions, high speed negativeplasticizers.

emulsions, X-ray emulsions, graphic are films, etc. If used withsensitizing dyes they may be added to the emulsion before or after thedyes are added. Various silver salts may be used as the sensitive salt,such as silver bromide, silver iodide, silver chloride or mixed silverhalides. Various other types of addenda such as stabilizers,anti-foggants, and the like may be used with these 7 The preferredcomposition of matter which is used in my invention is easily preparedby the simple esterification of available organic chemicals. Thefollowing preparation, using succinic acid asthe dibasic acid,illustrates the process of forming these compounds. 7

A one liter, '2 neck ground glass, round bottom flask was charged with205 grams of a mixture of diethylene 'glycol monoethyl ether andethylene glycol in a molar ratio of 1.221, 85 grams (0.72 mols) ofsuccinic acid, 200 m1. of benzene and 0.1 gram of p-toluene sulfonicacid as a catalyst. The flask was equipped with a Dean- Clark separatorfor the azeotropic removal of water using total reflux. The reactionmixture was refluxed until 92-94% of the theoretical amount of water wascollected based on the succinic acid. Ten grams of sodium carbonate werethen added to neutralize the mixture. After removing the carbonate byfiltration and washing the filter with a small quantity of benzene toremove adhering esters,-the mixture was concentrated, then extractedwith benzene, and vacuum distilled.

The resulting mixture was found to contain materials other than theesters of ethylene glycol and of diethylene glycol monoethyl ether,inasmuch as polymerization of some of the reaction products took place.

-The preferred composition of matter may be obtained by refluxing adibasic acid selected from the group consisting of succinic, adipic andphthalic acids with a mixture of 30-25% by weight ethylene glycol and70-75% by weight diethylene glycol monoalkyl ether having the followingformula:

CH (CH OCH CI-I OCH CH OH in which n is an integer of from 1 to 3 withthe removal of water until about 90% of the theoretical amount isremoved based on the esterification of the dibasic acid. Thiscomposition of matter maybe added to a'photo graphic film emulsion inanamount of SO -150% by weight based on the amount Of'gelatin in theemulsion.

The following examples are intended to illustrate but not to limit myinvention:

Example 1 tin, one part gelatin to approximately 10 parts pigment, I

no foam developed in the holding kettles or in the coating pan.

Example 11 A sample of paper containing a beater size of stearate soap,gelatin and starch was conditioned to equilibrium with 42% relativehumidity and coated as follows:'

Part A was given a tub size of 1 pound of gelatin per 3 gallons ofwater. Part B was coated'with 15%. of my preferred composition of matteras described in column 3, lines 9-43 and 1 pound of gelatin per 3gallons of water. These two samples were sensitized with a high contrastrecording type emulsion and were then slit into 35 mm; width rolls forelectric tests.

The following; electrification characteristics were tested: Surfaceresistivit-ies at three relative-humidities, electrificationcharacteristics in contact with'a polished stainlesS steel roller;electrification. characteristics in Willll Wit-ll 4 a Micarta(phenol-formaldehyde resin) roller, and electrification curves incontact with a cloth covered metal roller. The results of the testsshowed that the effectiveness of the bis (ethoxy diethylene glycol)increased as the concentration increased.

Example 111 T0. 470 grams of'a. photographic emulsion containing lightsensitive chloro-bromide silver salts and 8.5 gelatin by weight,suflicient of my preferred composition of matter as. described in column3, lines 9-43, was added to equal 50%, and of the' gelatin in theemulsion. Sufficient water was added to maintain the percent solidsequal in each emulsion part, and to resultin. equal solids laydownoneach part during coating. This emulsion was coated on glossy singleweight projection paper carrying a baryta-gelatin coating.

My preferred composition of matter as described in column 3, lines 9-43,was added to a high speed gelatinosilver bromide emulsion which was thencoated on a cellulose acetate support. Portions ofthis film were testedfor tackiness as compared with similar portions of a film to which hasbeen added glycerin as a plasticizcr with the following results: v

Ooncentra- Degree of Tackiness none.

. trace.

slight. had. none.

' none.

trace. no

Bis (ethoxy diethylene glycol) succinate was found to have little effecton the tackiness produced when as much as 16% was added to the film ascompared with glycerin, which is a well known plasticizer forphotographic emulsions. V

Ixhave found that the concentration of his (ethoxy diethylene glycol)succinate when used as a plasticizer is preferably equal to the weightof the gelatin vehicle in the pigment coating formulas, but /2 to 1times the amount of gelatin may be used. When used to reduce theelectrical resistivity of paper, a concentration .of 15% by weight inthe paper coating is preferred, but 530% may be used. As a dispersant offoam an amount equal to the gelatin in the pigment coating compositionis preferred, but /2 to 1 /2 that amount may be employed.

I also prefer to add an amount ofbis (ethoxy diethyl- 'ene glycol)succinate equal to the gelatin used in the pigment coating mixture, buta range of Vzto 1 /2 times maybe used. This material may be incorporatedinto the coated paper or into. uncoated paper by applying the his(ethoxy diethylene glycol) succinate in an after'treatment by immersingthe paper in asolution of a concentration of from 5% to. 30% based onthey total weight of paper treated. When used in a tubsize along withgelatin, the concentration may range from: 5% to 30%, of the totalsolution used. When used as a plasticizer in a photographic emulsion30-150% by weight of the gelatin can be used.

When the his (ethoxy diethylene glycol) succinate is added as thecoating compositions are first made up, this materialhas an opportunityto perform each of its functions. It can reduce foam in the coatingcomposition during the handling of the coating through successiveoperations of pumping to the coating pan, flowing on the paper and thelike. It also can plasticize the pigment coating after it has beenplaced on the paper and reduce stress and strain between the emulsionlayer which is coated over the pigment layer and the paper base beneaththe pigment layer. At the same time the his (ethoxy diethylene glycol)succinate also serves to reduce the electrical resistivity of the paperand lower the tendency of the paper to build up a static charge due topassing the paper over rollers and the like. When used with photographicpaper, bis (ethoxy diethylene glycol) succinate has a particularlybeneficial property in that it reduces static charges which can fog anemulsion with a discharge either during coating operations or operationsfollowing the coating.

Post-processing curl of photographic prints may be reduced by soakingthe photographic print in a solution of his (ethoxy diethylene glycol)succinate. Although various concentrations may be used, we prefer tosoak the prints from 1 to minutes in a concentration of from 5 to 30% byWeight of the solution.

Various other esters of glycol ethers may also be used, although thepreferred ester of a glycol ether is his (ethoxy diethylene glycol)succinate. Other which may be psed include bis (ethoxy diethyleneglycol) adipate, bis *{butoxy diethylene glycol) adipate, bis(butoxydiethylene glycol) phthalate, bis (ethoxy diethylene glycol) phthalate,and his (butoxy diethylene glycol) succinate.

Certain modifications may be made and these are intended to be includedwithin the scope of my invention. For instance, mixtures of thediethylene glycol monoalkyl ether and ethylene glycol may contain asmuch as 50 percent ethylene glycol or may contain only a few percent. Inaddition, for some purposes, the reaction products of esterifying thedibasic acid such as succinic acid, may be used without distilling themixture of reaction products. Normally, for photographic emulsions suchdistillation is desirable but for other applications such as theplasticization of paper, or the use in paper coatings where extremepurity is unnecessary, commercial grades of the ethylene glycolmonoalkyl ether which normally contain ethylene glycol, may be used toform the reaction products which I have found can be used for thepurposes disclosed herein.

It is believed that the reaction mixtures which may be obtained byesterifying the dibasic acids with the diethy1- ene glycol monoalkylether or by a mixture of the diethylene glycol monoalkyl ether andethylene glycol contain unreacted diethylene glycol monoalkyl ether,ethylene glycol and various esters of the dibasic acid as well aspolymerization products which are formed from these esters. However,nothing herein is intended to limit my invention to this particulartheory of operation, but on the contrary, it is intended that thereaction products formed by esterifying a dibasic acid with eitherdiethylene glycol monoalkyl ether or with a mixture of this ether andethylene glycol be included in the scope of this invention.

Since these compositions are soluble in water, we prefer to use water asa solvent. However, other solvents may be used such as ethanol,methanol, and the like. Bis (ethoxy diethylene glycol) succinate mayalso be incorporated in the final bath following the final washing ofthe prints in photographic processing.

This application is a continuation-impart of US. patent applicationSerial No. 532,756, filed September 6, 1955.

I claim:

1. A photographic emulsion containing light-sensitive silver halidesalts, and a composition of matter obtained by refluxing about 1 mol ofsuccinic acid with about 3 mols of a mixture of 30-25% by weightethylene glycol and -75% by weight diethylene glycol monoethyl etherwith the removal of water until about of the theoretical amount isremoved based on the esterification of the succinic acid.

2. A photographic gelatino-silver halide emulsion containing 30-150% byweight based on the gelatin content of a composition of matter obtainedby refluxing about 1 mol of succinic acid with about 3 mols of a mixtureof 30-25% by weight ethylene glycol and 70-75% by weight diethyleneglycol monoethyl ether with the removal of water until about 90% of thetheoretical amount is removed based on the esterification of thesuccinic acid.

3. A gelatino-silver halide emulsion containing 10-150% by weight basedon the gelatin content of a composition of matter obtained by refluxingabout 1 mol of a dibasic acid selected from the group consisting ofsuccinic, adipic, and phthalic acids with about 3 mols of a mixture of30-25% by weight ethylene glycol and 70-75% by weight diethylene glycolmonoalkyl ether having the following formula:

CH CH ,,OCH CH O CH CH OH in which n is an integer of from 1 to 3 withthe removal of water until about 90% of the theoretical amount isremoved based on the esterification of the dibasic acid.

References Cited in the file of this patent UNITED STATES PATENTS 71,714,173 Kessler et al. May 21, 1929 1,739,315 Kessler Dec. 10, 19291,966,856 Grofi July 17, 1934 2,232,707 Kendall Feb. 25, 1941 2,240,469Swan et al. Apr. 29, 1941 2,253,655 Shurley Aug. 26, 1941 2,376,005Potter et a1. May 15, 1945 2,388,164 Loder Oct. 30, 1945 2,394,198Mueller Feb. 5, 1946 2,400,532 Blake et al. May 27, 1946 2,444,607Heimbach July 6, 1948 2,764,609 Gamrath Sept. 25, 1956 2,778,850 Barr etal. Jan. 22, 1957

3. A GELATINO-SILVER HALIDE EMULSION CONTAINING 10-150% BY WEIGHT BASEDON THE GELATIN CONTENT OF A COMPOSITION OF MATTER OBTAINED BY REFLUXINGABOUT 1 MOL OF A DIBASIC ACID SELECTED FROM THE GROUP CONSISTING OFSUCCINIC, ADIPIC, AND PHTHALIC ACIDS WITH ABOUT 3 MOLS OF A MIXTURE OF30-25% BY WEIGHT ETHYLENE GLYCOL AND 70-75% BY WEIGHT DIETHYLENE GLYCOLMONOALKYL ETHER HAVING THE FOLLOWING FORMULA: